Swapping from 12-27 to 11-23
 

I've searched and searched and can't seem to get an answer to my questions.

I just ordered an Ultegra 11-23 10spd cassette to swap out my 105 12-27 10spd cassette. The wheels I'm using is a newer (08 to 2010) Mavic Kysrium Elites and I have a compact 105 crank.

-What size spacers do I need to make this work?

-Do I need to take out some links on my chain?

-Do I need to make any adjustments to my RD?

Thanks.

Keep exactly the same spacers the 12x27 now has as the 11x23 will need identical ones. I'm not sure what Mavic requires and Shimano provides a 1 mm thick spacer that goes behing their 10-speed cassettes when used on their 8/9/10-speed hubs. Anyway, keep what is already there in the same positions and order.

Going from a 27 to 23T big cog will let you remove 1/2 of the tooth difference of 4 teeth or 2 "half links" (i.e. 1") of chain.

You may need to make very minor limit screw and/or cable tension tweaks if the new cassette doesn't line up exactly with the old one. Try it with no adjustments first. Often none are needed.

As HillRider noted, you could remove links from your chain but you do not have to remove any links. Your small/small combo is only being reduced by one tooth so unless your chain was sized right at the limit of being too long, it won't be too long now.

27 to 23 will require a chain length drop, if your original chain was sized properly. R.D b-tension will also need to be readjusted, again assuming it was set properly.

Thanks for the help guys. When I took the cassette from my Mavics, there was a 2-3 mm spacer with cutouts that only fit one way. I installed the cassette both ways with and without this spacer and the play was eliminated with the spacer installed. Do you guys think I will still need to use the 1 mm spacer with that came with the 6700 Ultegra cassette.

That 1.1mm spacer is optional. The mavic spacer, is critical

Since when?

I also, again, disagree about shortening the chain. A chain with a few extra links isn't going to hurt anything. If the OP ever decides to swap back to the 12/27 cassette, they'll need to add links back to their chain (PITA) in order to use the bigger cassette. They gain nothing by shortening the chain (maybe a few grams).

Yes the Mavic spacer is mandatory.

Keeping two chains with SRAM quick link makes life easier for swaps.

You don't necessarily need a shorter chain, but you will notice better shifting with a shorter chain.

About as much as you'll notice a smoother ride from a carbon seatpost.

So, add the 1.1 mm spacer along with the Mavic spacer?

Yes, use the ~1mm spacer included with the cassette in addition to the Mavic spacer.